Public utilities use large amounts of underground electrical cable, such as electric power cable, telephone and telegraph cable, railroad and other public transportation cable systems, fire and police departments and traffic control signal generation cables, and the like. The preferred place of installation of cables of these type are below ground in conduits which protect the cables from weather and which do not disrupt the environment, either from an aesthetic point of view or from the very real practical problem of supporting many cables on overhead lines. Overhead lines have the further disadvantage of being susceptible to vandalism and present a real danger to the population in the event that cables fall due to accident, storms and the like.
However, even the best systems ultimately deteriorate. Underground cables either deteriorate and must be removed or replacement may be required by a cable which is either larger or which contains other features or which may be made from a different material. Even when cables are placed underground, there is a limit to the number of cables and conduits which can effectively be placed under city streets, for example, and so it is desirable to remove old cable. In addition, the new "information net work" that is said to be coming and the extensive increase in the use of fiber optic cables has made it desirable to replace cable presently existing with larger, faster, better or otherwise different cables.
One device which has been admirably suited as a apparatus for removing cable from underground conduits is shown in U.S. Pat. No. 3,736,822. In this patent, a cable puller is mounted on truck and placed near manholes and other underground locations for removing cable and cutting it into disposable length. An improvement of that prior patent is disclosed in U.S. Pat. No. 3,799,016, in which an improved puller and an improved cutter are disclosed.
In a more recent patent, U.S. Pat. No. 5,193,785, an extensible mechanism, such as a boom, is disclosed which allows the force directed on the cable as it is being pulled from the conduit to be axial and avoid tangential stress moments. It is much more effective in removing old or deteriorated cable which may be subjected to stress that cause rupture or breakage.
Once it was realized that old cable could be removed using these types of apparatus, it was attempted to use these same mobile vehicle to install new cable in the old conduits. However, this required significant down time as heavy new cable can only be pulled into a conduit after a substantial line such as a steel wire line has been attached to the cable through the conduit. Accordingly, effective utilization of the cable pulling device was not possible since there was no way to pull the wire using that device. Moreover, substantial modification of the cable pulling mechanism for removing old cable was necessary since the steel wire and the like attached to the new cable was not appropriate for use on the cable pulling devices as designed. Since the distance between adjacent cable access locations such as manholes may be as much as eight hundred feet or more, a large quantity of pulling wire rope is necessary to be stored when the cable puller is being used to remove old cable. In addition, that pulling wire rope must be readily accessible when the new cable is being installed.
In addition to the inability of the mobile cable pulling equipment to easily serve both removal and installation functions, there has been no attempt to coordinate the activity at the adjacent cable access location or manhole. Efforts to attach the new cable to the old cable prior to removal of the old cable have not met with success due to the extreme load place on the cable pulling device and due to the inability to inspect, clean, or otherwise maintain the conduit between removal and installation of the new cable. More importantly, the old cable is not normally strong enough to sustain the load necessary to pull a new cable into place in the conduit. When a steel wire rope is attached to the end of the old cable and pulled through when the old cable is removed, a new cable can be attached to the wire rope. This again leaves about eight hundred feet of steel wire rope to be handled by a separate pulling device, since the cable removing device is not suitable for pulling wire rope.
Accordingly, it is the object of the present invention to provide a system for removing cable and for installing cable using the same apparatus.
Another object of the present invention is to provide a modified cable pulling design which is capable of both removing and installing cable using the same means for pulling the old cable and the new.
Other objects will appear hereinafter.